1. Field of the Invention
This invention relates to an image reading apparatus for reading the image information of an original such as a photograph or a document and a method of assembling the same.
2. Related Background Art
FIGS. 5A, 5B and 5C of the accompanying drawings are a plan view, a cross-sectional view and a side view, respectively, schematically showing the construction of a colored image reading apparatus according to the earlier technology.
The letter P designates an original placed on an original supporting glass plate 100, and a reading unit 101 is scanned in parallelism to the original supporting glass plate 100 to thereby read an image on the original.
The reading unit 101, as schematically shown in FIG. 6 of the accompanying drawings, has incorporated therein LED""s of three colors (101R, 101G and 101B) which are light sources for irradiating the original, a rod lens array 101L for imaging the reflected light from the original on the light receiving element of an image sensor, and an image sensor 101S.
The light sources of three colors are successively changed over and turned on, and the image sensor reads the reflected light of each color from the original to thereby effect color separating and reading.
The reading unit 101 is fixedly supported on a slider 102 sliding on a guide shaft 103 fixed to the apparatus body. Also, a belt 104 for transmitting the motive power from a motor 105 which is a scanning drive source is fixed to the slider 102. By the forward and reverse rotations of the motor 105, the reading unit 101 can be reciprocally scanned within the image reading range of the original supporting glass plate 100.
The constituents of the image reading apparatus further include an electrically equipped portion 106 comprising a control board and a power source. These constituents are disposed in a housing comprising a combination of an upper cover 112 for fixedly supporting the original supporting glass plate and a lower cover 113.
An original cover 111 for pressing the original against the original supporting glass plate is openably and closably mounted on the original supporting glass plate 100.
FIG. 7 of the accompanying drawings is a read image data processing block diagram by the present image reading apparatus. An image output signal read by the image sensor 101S in synchronism with the LED""s successively turned on and off is sent to an amplifier 121 and is amplified thereby, whereafter it is converted into an image signal by an A/D converter 122.
The A/D converter 122 divides the dynamic range (the difference between the read outputs of the pure white portion and intense black portion on the original) of the image sensor into the number of bits thereof, and allots the number of gradation in conformity with the brightness of the image on the original. When for example, an A/D converter of resolving power of 8 bits is used, white to black can be discriminated into 256 gradation levels, and when an A/D converter of resolving power of 10 bits is used, white to black can be discriminated into 1024 dradation levels.
Accordingly, in an image reading apparatus using an A/D converter of 8 bits, 24 bits=about 16,700,000 colors can be discriminated in the cover reading by light sources of three colors R, G and B, and in the case of 10 bits, 30 bits=about 1,074,000,000 colors can be discriminated.
There are several kinds of output forms of the image signal of the image reading apparatus, and depending on the use of a read image, an output form suited therefor can be selected.
When a writing is to be read and its content is applied to OCR or when a monochromatic line drawing is to be read, a monochromatic binary image is suited therefor, and use is made of image data resulting from an image signal obtained with e.g. only G of the above-mentioned R, G and B light sources turned on having been binarized by a certain threshold value in an image processing circuit incorporated in a gate array 123.
When an image is to be read with a view to read an image such as a photograph and output it to a monochromatic printer, use is made of image data binarized by using an image signal also by the G light source and by the use of half-tone processing such as a dither method or an error diffusing method.
When the processing of a colored image is to be effected, image data of multiple values (such as 24 bits) is suitable.
The image signal passed through the image processing circuit is outputted to an apparatus 200 such as a personal computer through an interface circuit 124.
General as the construction of the housing of the above-described image reading apparatus is a two-piece construction in which the upper cover 112 made of resin on which the original supporting glass plate 100 is mounted is put on the lower cover 113 made of resin on which the constituents are placed.
However, the covers made of resin has the disadvantages that their cost is high and moreover they are weak in rigidity and are difficult to provide dimensional accuracy.
Accordingly, it has been necessary to cope with it by a construction in which the covers are provided with a number of reinforcing ribs to secure rigidity or a designing technique for making the structure of the place constituent side firm and difficult to deform.
Also, the constituent for effecting reading scan is placed on the lower cover 113 and thus, the upper cover 112 intervenes between it and the original supporting glass plate 100, and the dimensional accuracy of the upper cover 112 had the possibility of affecting the scanning parallelism to the original supporting glass plate 100.
The present invention has been made in order to solve the above-noted problems peculiar to the earlier technology and an object thereof is to provide an image reading apparatus which is inexpensive and easy to provide dimensional accuracy as well as high in rigidity.
Another object of the present invention is to provide an image reading apparatus having a transparent plate for supporting an original thereon, a reading unit for reading the original, and a one-piece frame member containing the reading unit therein.
Still another object of the present invention is to provide a method of assembling an image reading apparatus having the step of mounting a reading unit on a frame member, the step of inserting the fore end of a transparent plate for supporting an original thereon into the transparent plate holding portion of the frame member, and the step of dropping the rear end of the transparent plate onto the frame member.